Method for calcining crude lithopone



A. S. KREBS METHOD FOB CALCINING CRUDE LITHOPONE Filed April 14, 1923 Patented Aug. 25, 1925.

UNITED 'STATES AUGUST soNNI'N xnEBs, Or `J WILMINGTON,y DELAWARE, AssrNon TO xnEBs PIGMENT e CHEMICAL COMPANY, or NEWPORT, DELAWARE, A CORPORATION or nELAwAnE. y

METHOD Eon CALCINING CnUnE EITBOPONE,

\ g Application med Apri1f14, 192s. serrai No, 682,645.

To all 'whom z't may concern.

Be it known that I, 'AUGUST SONNIN KREBs, a citizen of the United States of America, and resident of Wilmington, county of Newcastle, State of Delaware, have invented a certain new and useful Improvement in Methods for Calcining Crude Lithopone, of which the following is a true and exact description, reference being had to the accompanying drawing, which forms a part thereof.

This invention relates to processes` of manufacturing lithopone; and it has to do more particularly, though not in all respects exclusively, with the calcination of crude lithopone in a continuous rotary furnace, most desirably of the mulile type, wherein the conditions of Calcination are so controlled and regulated as to insure the production` of high grade lithopone in a simpler, more dependable and more economical way than has been available heretofore.

In the manufacture of lithopone, purified liquors or solutions of barium sulphlde and Zinc sulphate are brought together in the precipitating or strike vats in the proper proportion and under proper conditions to produce a mixed precipitate of barium sulphate and zinc sulphide, which, after washing and more or less complete drying, constitutes what is known as crude lithopone.

Long experience in the manufacture of lithopone by old methods and apparatus and protracted experiments and tests with new methods and apparatus has demonstrated that a uniformly excellent product depends very largely on the conditions existing during the calcination of the crude lithopone which must be such that the mass under 'treatment in all its parts is uniformly heated and maintained at the necessary or desirable calcining temperature for a necessary period and these conditions have been found to require that the mass while being raised to and maintained at the necessary temperature should be constantly tumbled and mixed so that no portion remains in constant contact with Cr fixed relation-to the walls of the furnace chamber and all portions are exposed to the same heating conditions. It has also been found that for uniform good results itis highly desirable -that the mass under treatment should for reasons be maintained -in a comparatively f thick ybed'or layer in the furnace and for this and other reasons it has been found advisable to maintain in the rotating approxlmatelyz horizontal muiile, which it is preferred to use, a charge approximately half the cubic capacity of the muiile. In a rotating mulile through which the lithopone 1s fed this condition is conveniently maintained by providing the vmuile with a. centrally located outlet orifice Aof small diameter at its outer end. A further ob- ]ect of m invention is to prevent the ladherence of/particles of litho one to the walls of the mu e furnace. ven where the muiile consists of a metal tube with smooth orunpolished inner walls there is a tendency fon particles of litho one to adhere to the wall, land consequent y not mix with the bulk of the tumbling charge,cons uently such particles become overburned an moreover such adhering particles tend to promote the adherence of other particles and cause the formation of overburned crus'ts. It has been found that the adherence of lithopone particles to the furnace wall can be prevented by causing vibrations to occur in the Walls of the metal muifle at comparatively short intervals; such vibrations shake loose the adhering particles and insure that alll parts of the char e shall he calcined under similar and the est conditions.

Another object of. the invention is to provide a method of calcining lithopone in which the lithopone after having been raised to the necessary or desirable temperature4 'or an extension of the mulile, so as to lessen the tendency to form zinc oxide on the exposure of the hot lithopone to the air.

The nature of the invention both as a new method and as to apparatus designed for the Iet practice of the method invention will be best periodically rapping the metallic muflie to cause vibration in its walls.

A is thel heating furnace, B an 011 ]et. C,

C, walls supporting rollers C which in turn support the tubular mufile D, through the metallic ring or tires E, E. F is an extensionl of the mufile C lying outside of furnace A, and having a heat insulating jacket F. G is a delivery orifice centrally located in the end of the mule tube and of small diameter. H is a hopper having a tubular delivery spout H in which works a conveyor I, the shaft I of which has a sprocket wheel I2 secured to it. J is a sprocket wheel secured to the mule D. K is a driving shaft having sprockets K and K2 which, through chains L and L drive sprockets I and J. M is a lever pivoted on shaft K carrying on its free end a 'weighted roller M which registers with the lifting cams N secured to the mule, as shown in Fig. 2.

O is an air cooled mufle extension having external ribs O and a centrally located restricted discharge opening g. P is a belt conveyor for carrying away the calcined lithopone. Q and Q are thermocouples. R indicates the level of the lithopone in' the muie.

In operation the crude lithopone is charged into the hopper H and fed from this hopper into the receiving end of the rotating muflle Dv by the action of the conveyor indicated at I. The construction at the receivingend of the mufile is such as to exclude air. The muffle D is kept in constant rotation by the ,described mechanism and may be slightly inclined toward its outer end to facilitate the travel of the lithopone through it. As the lithopone travels through the muffle it is gradually raised to proper calcining temperature which it is preferred to maintain moderately low, say between 550 and 750o C., although it is feasible to use somewhat lower temperatures and a temperature of as high as 900 C. or thereabouts may be employed under some circumstances.A The time of treatment will naturally vary with the temperature to which the lithopone is raised but within the range of temperatures preferred the period of calcination will be in the neighborhood of from fifty to twenty-five minutes. The lithopone is maintained in the rotating muflie in acomparatively deep layer or bed approximating half the cubic capacity of the mufile and thisy is best accomplished by providing the delivery end of the mufiie with a centrally located Ias indicated at G.

delivery orifice of relatively small diameter, The exact proportion and volume of the lithopone to the cubic capacity of the mufile is not at all important so long as a bed or layer of substantial thickness is maintained.

The lithopone under treatment is, in the apparatus shown, constantly stirred and tumbled by the rotation of the -muffle and this tumbling action is of great importance in securing substantially uniformity of condition and exposure to heat 'of the whole mass of lithopone under treatment.

The tendency of particles oflithopone to adhere to the walls ofthe mufiie and become over-burned is overcome by causing frequent vibrations in the walls of the metallic mufiie and a convenient device for striking frequent periodical blows causing such vibration isthe weighted lever M which is raised by the cams N and periodically allowed to fall upon the muflle D.

I have, as already stated, discovered that material advantages are secured by permitting the lithopone after it is raised to the desired calcining temperature to soak in its own heat lfor a period before its final delivery out of the muffle. Such a heat soaking of the lithopone is provided for in the apparatus shown by the muffle attachment F having a heat insulating jacket F which is attached to the mufiie outside of the furnace A so that, after being raised tothe proper temperature the lithopone in the extension F is permitted to soak in its own heat While being constantly agitated and tumbled a it is in the muflie itself.-

It is, I believe, advantageous in calcining lithopone in a mufile of Whatever construction and mode of operation that the lithopone fore it escapes from the atmospheric condi-' tions existing in the muflie. This I provide for by attaching fo the end of the mufile a cooling extension indicated at O which, as shown, is intended to beair cooled and provide ribs O but which, of course, can be cooled in any convenientway. This extension, as shown, is secured to' the end ofthe extension F and rotates with themufile and is provided with a centrally located delivery orifice g of small diameter so that the conditions as to 'tumbling and thickness of the layer are maintained in this extension. In the construction rshown lthe small delivery orifice G or g insures not onl that a properly deep bed of lithopone s ould be maintained but also provides against the entrance of air at the delivery end ofthe mufile and its extensions. a constantoutward current of gas and vapors generated in the mufl'le passing through the small delivery orifices.

This apparatus described embodies also newly invented `features which are the subject matter of my application filed June 21, 1924, Serial Number 721,436. .l

Having now described my inventlon, what I claim as new and desire to secure by Letters Patent, is:

1. The method of calcining crude lithoone which consists in charging the crude 'thopone into a substantially. horizontal tubular rotating furnace maintained at calcining temperature, regulating the amount of the furnacecharge so that it will not substantially exceed half the cubic capacity of the furnace, vconstantly stirrin and turning the charge by the' rotation o the furnace and maintaininga substantially non-oxidizing atmosphere in the furnace during the calcination of the charge.

2. The method of calcining crude lithopone which consists in charging the crude lithopone into a substantially horizontal tubular rotating furnace maintained at calcining temperature, regulating the amount of the furnace charge so that it will not substantially exceed half the cubic capacity of the furnace, constantly stirrin and turning the charge by the rotation o the furnace, preventing adhesion of particles `of the charge to the furnace walls by causing said walls to vibrate and maintaining a substantially non-oxidizing atmosphere in the furnace during the calcination of the charge.

3. The method of calcining crude lithopone which consists in charging the crude lithopone into a substantially horizontal tubular rotating furnace, maintaining a calcining temperature in said furnace by heat transmitted through the walls thereof, regulating the amount of the furnace charge so that it will not substantially exceed half the cubic capacity of the furnace, constantly stirring and tumbling the litho one under treatment by the rotation of the urnace and maintaining a substantially non-oxidizing atmosphere in the furnace during the calcination of the charge.

4. The method of calcining crude lithonone which consists in continuously charging the crude lithopone into one end of a substantially horizontal tubular rotating furnace causing the lithopone. to move continuously through the furnace to a discharge opening at its other end, regulating the feed of lithopone into and through the furnace so that it will not occupy 'substantially more than half of the cubic capacity of the furnace, maintaining a calcining temperature in said furnace by heat transmitted through the walls thereof, constantly stirring and tumbling the lithopone under treatment by the rotation of the furnace, preventing `adhesion of particles of lithopone `to the Walls of the furnace by causing said walls to vibrate and maintaining-a substan- Vtially non-oxidizing atmosphere in the furnace during the calcination of the charge.

5. The method of calcining `crude lithoponewhich consists in continuously charging crude lithopone into one end of a horizontal rotating tubular furnace, continuously feeding the lithopone through the furnace to a discharge opening at its other end, maintaining the lithopone in the furnace in a deep bed approximately but not materially exceeding half the cubic capacity of the furnace, maintaining the furnace at calcining temperature by heat transmitted through the Walls of the furnace, maintaining a substantially non-oxidizing atmosphere in the furnace andcontinuously tumbling the deep charge in the. furnace y the rotation of the furnace.

6. The method of calcining crude lithopone which consists in continuously charging crude lithopone into one end of a horizontal rotating tubular furnace, continuously feeding theA lithopone through the furnace to a discharge opening at its other end,maintaining the lithopone in the furnace in a deep bed approximately but not materially exceeding half the cubic capacity of the furnace, maintaining the furnace at calcining temperature by heat transmittedthrough the `Walls of the furnace, maintaining a substantially non-oxidizing atmosphere in the` furnace continuously tumbling the deep charge in the furnace by the rotation of the furnace and preventing the adherence of lithopone particles to the furnace.

Waiis by causing vibration of the furnace Wa 7 The method of calcining crude litho-I pone which consists in continuously char ing crude lithopone into one end of a horizontal rotating tubular furnace in a stream of small section, maintaining the lithopone in the furnace in a layer approximately but not materially exceeding half the capacity of the furnace by causing it to discharge in a thin stream through a small centrally located opening at the discharge end of the furnace, heating the charge by heat transmitted through the Wall of the furnace, maintaining a substantially non-oxidizing atmosphere in the furnace and continuously tumbling the furnace charge by the rotation of the furnace.

8. The method of calcining crude lithopone which consists 'in feeding it through a horizontal rotatable tubular furnace, maintaining the lithopone in a deep bed in the furnace, heating the charge by `heat transmitted through the front portion of the Walls of the furnacebut not through the Walls of the rear or delivery end thereof, permitting the calcined charge to soak'in its o wn heat asit passes through the unheated end of-.the furnace, tumbling the lll charge throughout the length of the furnace by rotating the furnace and maintaining a substantially non-oxidizing atmosphere throughout the furnace.

9. The method of calcining crude lithopone which consists in feeding it longitudinally through an externally heated mufile in a substantially non-oxidizing atmosphere and cooling the calcined productby passing it through an externally cooled muie extension in'which the non-oxidizing atmosphere is also maintained. a

l0. The method of calcining crude lithopone whichv consists in feedingit longitudinally through an externally heated muflle permitting the calcined product to Soak in its own heat as it passes through a rear nonexternally heated section of the 'muflie in a substantially non-oxidizing atmosphere and cooling the calcined product by passing it through an externally cooled mule extension in which the non-oxidizing atmosphere isl also maintained.

11. The method of calcining crude litholpone which consists in feeding it through a orizontal rotatable tubular furnace, maintaining the lithopone in a deep bed in the furnace, heating the charge by heat trans-A mitted through the front portion .of the Walls of the furnace but not through the walls of the rear or delivery end thereof,

permitting the calcined charge to soak in its .and its 'extension lby rotating the furnace and maintaining asubstantially non-oxidizing atmosphere throughout the furnace and its extension.-

12. The method of calcining crude lithopone which consists inpassing it through a horizontal externally heated rotatable tubular furnace in a deep layer, heating the charge by heat transmitted through' the Walls of the furnace, continuously tumbling the charge in the furnace by the rotation of the furnace, 'cooling the calcined lithopone by passing it through an externally cooled furnace extension and maintaining a substantially non-oxidizing atmosphere in the furnace and its externally cooled extension.

' A. soNNiN KREBS. 

